On Tuesday morning, rescuers rushed 21-year-old Alexandra Tobias's 3-month-old son Dylan to a hospital. Police said the boy had a head injury and a broken leg.

Police later interviewed Tobias and said she admitted to shaking the baby because he was crying while she played a game on Facebook. Police said Tobias shook the baby three times, and the baby's head could have hit the computer.

According to police, Tobias went outside to smoke a cigarette, and while she was out, the family dog knocked the boy off the couch.

Investigators said when she came back in, the boy cried again and police said she admitted to shaking the boy again, causing him to stop breathing.

Police first arrested Tobias on Tuesday for aggravated child abuse. After her son died Wednesday, they added the charge of murder.

The baby's father said Tobias called him initially after the baby was injured, and he said he wasn't as angry or sad as he was in shock over what happened.

"I think what sparked her was that the baby was crying," Jacksonville Sheriff's Office Lt. Larry Schmitt said. "I don't think it mattered what she was doing, but it was enough to kind of put her over the edge, and she started shaking the baby, caused severe head trauma to the child."